This will be an adventure for 4-6 brave (and probably foolish) adventurers, at level 3. Core PHB and Unearthed Arcana will be permitted sources of race/class/feats/spells, and for stats we're going to do it classic-style (roll 4d6, drop lowest).
For a free bonus feat, you can roll your attributes in place (that is, your first roll is assigned as Str, second Dex, etc...). You don't have to pick race/class until after you roll (that would be beyond mean).
Discussion about characters here, as well as your stats rolls. For equipment, as you will be level 3, it is safe to assume you have had the opportunity to get whatever you need. I will permit you to eschew starting equipment and instead pick any 1 armor, up to 4 'hands' worth of weapons/shields and a 'reasonable' amount of adventuring gear (you could just pick a pack or two and call it a day). If you want something like '10 daggers' and a bandolier, we can discuss that. Basically, your character should be reasonably equipped.